Superman's Metropolis is inspired by the silent German Expressionist film, Fritz Lang's Metropolis.

A fourth volume, The Green Light, was planned, but remains unpublished. It would have featured Aquaman, The Flash, Green Lantern and the Martian Manhunter, and would have been based upon the films, Das Blaue Licht, Weiße Rausch - Der Neue Wunder des Schneeschuhs (aka The White Flame), and Die Herrin von Atlantis (aka The Mistress of Atlantis).